1. Field of the Invention
The present invention relates to a toner for use in a developer for developing an electrostatic latent image in electrophotography, electrostatic recording, electrostatic printing, etc., and to an image forming apparatus and a process cartridge using the toner. More particularly to a toner for developing an electrostatic image for use in copiers, laser printers, plain paper facsimiles, etc. using direct or indirect electrophotographic developing method, an image forming apparatus and a process cartridge using the toner, and to a method of preparing the toner.
2. Discussion of the Background
Recent strong demands for higher quality images from the market spur development of suitable image forming apparatuses and a developer (toner) for use therein.
The toner for higher quality images needs to have a uniform particle diameter. This is because when a toner having a sharp particle diameter distribution, individual toner particles uniformly move to largely improve microscopic dot reproducibility.
However, it has conventionally been difficult to stably clean a toner having a small and uniform particle diameter, and particularly a blade cleaner is very difficult to clean the toner having a small and uniform particle diameter.
In this circumstance, various methods of designing a toner to improving the cleanability thereof are considered.
One of the methods is changing the shape of a toner from a sphere to an irregular shape. A toner having an irregular shape has low fluidity and is easily dammed by a cleaning blade. However, when the shape of a toner is too irregular, the toner irregularly behaves, resulting in deterioration of microscopic dot reproducibility.
As mentioned above, although the toner having an irregular shape has reliable cleanability, the toner is difficult to transfer.
In order to improve transferability and cleanability of a toner, Japanese published unexamined application No. 3-100661 discloses a toner including a specific amount of two inorganic particulate materials as external additives having an average particle diameter not less than 5 mμ and less than 20 mμ, and from 20 to 40 mμ, respectively. Although the toner initially has high transferability and cleanability, the external additives are easily buried or peeled, resulting in large deterioration of the transferability and cleanability.
Japanese published unexamined applications Nos. 7-28276 and 9-319134 disclose that an inorganic particulate material having a large particle diameter is effectively used to prevent them from being buried in a toner (colored particulate material). Having a large specific gravity, the inorganic particulate material having a large particle diameter does not adhere well to a toner and easily leaves therefrom, resulting in longer life of a cleaning blade.
It is thought that this is because the free inorganic particulate material having a large particle diameter between the blade edge and a photoreceptor forms an exquisite dam to largely decrease an abrasion therebetween. The present inventors are aware that an inorganic particulate material having a primary particle diameter not less than 200 nm is likely to leave from a toner and involved with forming the dam to maintain the cleanability. An inorganic particulate material having a primary particle diameter of from 80 to 200 nm has been conventionally said to prevent an external additive from being buried in a toner, and adheres on a toner to maintain the transferability.
The free inorganic particulate material having a large particle diameter is coated on a photoreceptor, resulting in filming thereover. Japanese published unexamined application No. 2001-66820 discloses the inorganic particulate material having a large particle diameter and an order of adding an external additive, but does not balance between forming the dam and preventing the filming. Particularly, the filming noticeably affects the resultant image quality at a high temperature and is desired to be higher technologically solved. Japanese published unexamined application No. 2001-13837 discloses a method of forming the dam, but needs an exclusive external additive applicator and is difficult to save space and cost. In addition, it is inconvenient that the external additive needs to be exchanged separately. Japanese published unexamined application No. 2002-196526 discloses specifying a particle diameter distribution of an external additive on the surface of a toner. Namely, the toner includes the external additive having a particle diameter of from 0.005 to 0.025 μm in an amount of 65 to 95% by weight, 0.025 to 0.080 μm in an amount of 4 to 35% by weight, and 0.080 to 0.500 μm in an amount of 0.3 to 10% by weight to prevent the external additive from being buried and produce high-definition images without contamination. However, the external additive having a particle diameter of from 0.080 to 0.500 μm, which is likely to leave from the toner, is not mentioned and an action against the filming over a photoreceptor is not fully performed.
Because of these reasons, a need exists for a toner for developing electrostatic latent images, having high cleanability, transferability with less untransferred toner and filming resistance, and stably producing high-quality images having good microscopic dot reproducibility even at a high temperature and/or a high humidity.